Thing I notice most I think is a lot less often there is a 1-2 hour slot sometimes it is just "all day" though they try and dress it up like it is a more specific timeslot. Though that change might somewhat be due to moving to a more rural area vs when I lived in a city or town but even when we first moved here the timeslots were more specific.
That's definitely one frustrating thing with Amazon. They'll give a delivery slot of maybe between 2 hours. It gets closer to that window and it gets bumped back another hour. Another hour goes past and it gets bumped again.
Surely their systems - especially with the amount of deliveries they do, must be able to better predict that an original schedule was unrealistic.